Control structure for electro-mechanical camshaft phase shifting device

ABSTRACT

A camshaft phase shifting device ( 30 ) includes a coaxially arranged three-shaft gear system, having an input shaft ( 16 ), an output shaft ( 14 ), and a control shaft ( 34 ) for adjusting the phase angle between the input and output shafts ( 16, 14 ). The control structure is a torque-based control structure. The dynamic response of the gear system and thus the desired phase angle of a camshaft ( 12 ) associated with the output shaft ( 16 ) is controlled and adjusted by a controller ( 40 ) which produces a torque command based on received signals. These signals include, but are not limited to, cam shaft phase angle error signal, torque load, and/or angular position signal of the camshaft ( 12 ), and relative speed signal between the input and output shafts ( 16, 14 ). The torque command is converted by an electric machine ( 32 ) into an electro-magnetic torque exerting on the control shaft ( 34 ) of the camshaft phase shifting device ( 30 ), and includes two parts, a feed forward part to compensate for the known disturbances in system torques and a feedback part to compensate for unknown disturbances.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to, and claims priority from, U.S.Provisional Patent Application Ser. No. 60/868,644 filed on Dec. 5,2006, and which is herein incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention is related generally to a camshaft adjustmentmechanism for use in an internal combustion engine, and in particular,to a control structure for an electro-mechanical camshaft phase shiftingdevice.

Camshaft phase shifting devices are used more often in gasoline enginesto vary valve timing for benefits of improving fuel consumption andexhaust gas quality. There are many types of cam shaft phase shiftingdevices. Hydraulic adjusters are commonly seen in many currentapplications. The major challenges for hydraulic adjusters includesimproving slew rate in slow-speed operation, maintaining accuratecamshaft angular position, and extending the operating temperaturerange. In addition, to reduce high pollutant emissions, it is highlydesirable to adjust the cam phase angle before or during engine startup.This requires the camshaft phase shifting device to be controlled priorto or during engine startup. These challenges can only be met byelectro-mechanical camshaft phase shifting devices.

In co-pending WO International Application No. PCT/US2007/078755(Continuous Camshaft Phase Shifting Apparatus) filed on Sep. 18, 2007and herein incorporated by reference, an electro-mechanic camshaft phaseshifting device (eCPS) is disclosed. The eCPS device includes athree-shaft gear unit and an electric machine. According to the demandfrom engine electronic control unit (ECU), the electric machine isoperated in one of three available modes, the neutral operating mode,the motoring mode, and the generating mode, to achieve desiredperformance objectives. The present invention discloses a controlstructure that provides a concrete means for an eCPS device to realizethese operation modes. The disclosed control structure may additionallybe applied to regulate the operation of other similar electro-mechanicalcamshaft phase shifting devices.

BRIEF SUMMARY OF THE INVENTION

Briefly stated, the present disclosure provides a control structure forelectro-mechanic camshaft phase shifting devices in general and acontrol structure for an electro-mechanic camshaft phase shifting devicewith a self-locking mechanism in particular.

In an embodiment of the present disclosure, the camshaft phase shiftingdevice includes a coaxially arranged three-shaft gear system, having aninput shaft, an output shaft, and a control shaft for adjusting thephase angle between the input and output shafts. The control structureis a torque-based control structure. The dynamic response of the gearsystem and thus the desired phase angle of camshaft is controlled andadjusted by a controller (or compensator) which produces a torquecommand based on received signals. These signals include, but are notlimited to, cam shaft phase angle error signal (deviation of cam phaseshift angle from the reference value), torque load, and/or angularposition signal of the cam shaft, and relative speed signal between theinput and output shafts. This torque command (a voltage signal forexample) is then converted by an electric machine into anelectro-magnetic torque exerting on the control shaft of the camshaftphase shifting device. The torque command includes two parts, a feedforward part to compensate for the known disturbances in system torquesand a feedback part to clear up unknown disturbances and to trackreference change. Optionally, the controller may include an on-and-offswitch to turn off the torque command for energy savings whenself-locking mechanism is determined active.

The foregoing features, and advantages set forth in the presentdisclosure as well as presently preferred embodiments will become moreapparent from the reading of the following description in connectionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the accompanying drawings which form part of the specification:

FIG. 1 illustrates a block diagram of a preferred control structure forcontrolling an electro-mechanical cam phase shifting device of thepresent invention;

FIG. 2 is a sectional view of an electro-magnetic cam phase shiftingdevice;

FIG. 3 is an input-output diagram for the control structure of FIG. 1;

FIG. 4 illustrates a block diagram of an alternate control structure forcontrolling an electro-mechanical cam phase shifting device of thepresent invention.

Corresponding reference numerals indicate corresponding parts throughoutthe several figures of the drawings. It is to be understood that thedrawings are for illustrating the concepts set forth in the presentdisclosure and are not to scale.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following detailed description illustrates the invention by way ofexample and not by way of limitation. The description enables oneskilled in the art to make and use the present disclosure, and describesseveral embodiments, adaptations, variations, alternatives, and uses ofthe present disclosure, including what is presently believed to be thebest mode of carrying out the present disclosure.

Turning to the figures, and to FIG. 1 in particular, a preferred controlstructure for controlling an electro-mechanical cam phase shiftingdevice is shown generally. The system shown in FIG. 1 is comprised of anengine 10, an engine control unit (ECU) 20, a phase shifting device 30,and a controller (or compensator) 40. The phase shifting device 30 is athree-shaft, positive differential gear drive, having three co-axiallyarranged rotate-able shafts, as is depicted in FIG. 2. The input shaft16 is connected through sprocket 18 and a chain drive (not shown) toengine crank shaft. The output shaft 14 is connected to engine cam shaft12. The control shaft 34 is coupled to the rotor of an electric machine32.

The phase shifting device has a built-in frictional self-lockingmechanism, which enables the output shaft 14 to lock-up with the inputshaft 16, and therefore to transmit torque between the two shafts with a1:1 speed ratio. Under this condition, there will be no phase shiftbetween input shaft 16 and output shaft 14. Frictional locking betweenthe input shaft 16 and the output shaft 14 can only be unlocked byapplying an adequate toque to the control shaft 34. The required torqueis generated by the electric machine 32 coupled to the shaft 34 inresponse to a torque command received by the electric machine. When thephase shifting device is unlocked, there may be a slight differencebetween the input and output shaft speeds. This allows the cam shaftconnected to the output shaft 14 to shift in angular position withrespect to the input shaft 16.

The controller (or compensator) 40 generates the torque command, whichcan be in the form of a voltage signal or any other suitable signalform, based on information received by the controller (or compensator)40. The received information may include, but is not limited to, a camshaft phase shift set point (reference), or an actual cam shaft phaseshift measured and/or computed from one or more angular position sensorsignals. The actual cam phase shift angle is compared to a referencevalue to generate a differential (error) signal. The differential orerror signal is then communicated to a PID compensator 42 to generate afeedback torque (torque adjustment) command. This feedback torquecommand in turn is used to direct the electric machine for controllingand adjusting the cam phase angle to reduce the error signal to theinput of the PID compensator 42. In doing so, the desired cam phaseshift is archived. For a torque based control structure, the PIDcompensator is primarily a proportional-and-derivative controller (PD).

In engine applications, there may be disturbances to the control system.Shaft torque varies as a function of cam phase angle during valve liftevents. To improve the system response to a reference input and theability of the system to identify and/or reject disturbances, it oftenis desirable to use a feed-forward scheme to compensate any knowndisturbances. Therefore, controller (or compensator) 40 may furtherinclude a feed-forward branch (or a unit) 44 for processing andcomputing the anticipated torque disturbances within the system. Theresulting signal is fed forward to, and combined with, the output signalof the PID controller, forming the torque command signal. Theanticipated torque disturbance, also referred to as feed-forward torque,is determined from two components, T_(rq) _(—) _(static) and T_(rq) _(—)_(friction). T_(rq) _(—) _(static) is calculated from the frictionlessstatic equilibrium condition of the three-shaft gear drive, while T_(rq)_(—) _(friction) represents the component required to overcome thefrictional torque for a current cam shaft torque load. The sign ofT_(rq) _(—) _(friction) is determined by the relative speed between thecontrol shaft 34 and the input shaft 16 (or the output shaft 14). Forthe disclosed configuration of phase shifting device shown in FIG. 2,the feed-forward torque is calculated as

T _(ffwd) =T _(rq) _(—) _(static) +T _(rq) _(—) _(friction)=(1−SR ₀)·T_(cam) +sgn(v)·f(T _(cam))

where T_(cam) is the cam shaft torque load, which is a function of camphase angle and which can be expressed by an analytical equation or by alook-up table. The value sgn(v) represents sign of relative speed vbetween the control shaft 34 and the input shaft 16, while the functionf(T_(cam)) represent the magnitude of the frictional torque T_(rq) _(—)_(friction).

SR₀ is the base speed ratio of output shaft 14 to the input shaft 16,given by following equation

${SR}_{0} = {\frac{N_{S\; 1}}{N_{S\; 2}} \cdot \frac{N_{P\; 2}}{N_{P\; 1}}}$

where N denotes the number of gear teeth with its subscripts_(S1, S2, P1,) and _(P2) representing the first sun gear 31 coupled tothe input shaft 16, the second sun gear 33 coupled to the output shaft14, the first planet gear 35 engaging the first sun gear 31, and thesecond planet gear 37 engaging the second sun gear 33, respectively. Asshown in FIG. 2, the first and second planet gears 35, 37 are integrallyformed with, and carried on a common planet assembly 39 which issupported by, and rotates with, the control shaft 34.

Since, as described before, the phase shaft device features aself-locking mechanism, it is possible to turn the controller and theelectric machine off for energy savings when the actual cam phase shiftangle is in a close proximity to the desired value (a reference value ora set point). This is done, for example, by commanding a zero torque tothe electric machine. FIG. 3 illustrates an alternate implementation ofthe controller 40 in simulation, where a power-on logic and power switchare shown in separate blocks.

Optionally, the derivative portion of the PID compensator may be movedto the feedback path to reduce the effects of impulses (sudden changes)in reference input. FIG. 4 shows the corresponding control structure forthis optional configuration.

It is also possible to use other type of compensators with alternativecontrol laws, such as model predictive controller (MPC), to replace thePID compensator 42, and the current invention may include otherembodiments that can be derived from the current torque based controlstructure.

The present disclosure can be embodied in-part the form ofcomputer-implemented processes and apparatuses for practicing thoseprocesses. The present disclosure can also be embodied in-part the formof computer program code containing instructions embodied in tangiblemedia, such as floppy diskettes, CD-ROMs, hard drives, or an othercomputer readable storage medium, wherein, when the computer programcode is loaded into, and executed by, an electronic device such as acomputer, micro-processor or logic circuit, the device becomes anapparatus for practicing the present disclosure.

The present disclosure can also be embodied in-part the form of computerprogram code, for example, whether stored in a storage medium, loadedinto and/or executed by a computer, or transmitted over sometransmission medium, such as over electrical wiring or cabling, throughfiber optics, or via electromagnetic radiation, wherein, when thecomputer program code is loaded into and executed by a computer, thecomputer becomes an apparatus for practicing the present disclosure.When implemented in a general-purpose microprocessor, the computerprogram code segments configure the microprocessor to create specificlogic circuits.

As various changes could be made in the above constructions withoutdeparting from the scope of the disclosure, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

1. A camshaft phase shifting device comprising: a coaxially arrangedthree-shaft gear system, having an input shaft, an output shaft, and acontrol shaft, said control shaft configured to adjust a phase anglebetween said input shaft and said output shaft; a friction self-lockingmechanism responsive to said control shaft to selectively phase-locksaid input shaft and said output shaft; and a controller operativelycoupled to said control shaft, said controller responsive to at leastone input signal to regulate a source of an applied electro-magnetictorque to said control shaft to control said friction self-lockingmechanism to unlock the phase angle of said input shaft relative to saidoutput shaft.
 2. The camshaft phase shifting device of claim 1 whereinsaid controller operates with a torque-based control structure.
 3. Thecamshaft phase shifting device of claim 1 wherein said controller isconfigured to generate a torque command to said source of appliedelectro-magnetic torque in response to said at least one plurality ofinput signal.
 4. The camshaft phase shifting device of claim 1 whereinsaid at least one input signal is selected from a set of input signalsincluding, but not limited to, a cam shaft phase angle error signal, atorque load signal, an angular position signal of the cam shaft, andrelative speed signal between the input and output shafts.
 5. Thecamshaft phase shifting device of claim 1 wherein said source of appliedelectro-magnetic torque is an electric machine configured to exert saidelectro-magnetic torque on said control shaft, said electric machineregulated by a torque command from said controller.
 6. The camshaftphase shifting device of claim 5 wherein said torque command includes atleast a feed-forward component to compensate for known disturbances insystem torques, and at least a feedback component to compensate forunknown disturbances and to track reference input.
 7. The camshaft phaseshifting device of claim 6 wherein said feed-forward component of saidtorque command is calculated as:T _(ffwd) =T _(rq) _(—) _(static) +T _(rq) _(—) _(friction)=(1−SR ₀)·T_(cam) +sgn(v)·f(T _(cam)) where T_(rq) _(—) _(static) is the torqueload reflected on the control shaft based on frictionless staticequilibrium condition of the phase shifting device; T_(rq) _(—)_(friction) is the force required to overcome the frictional torquecorresponding to the current control shaft torque load; SR₀ is the basespeed ratio of the output shaft relative to the input shaft; T_(cam) isthe cam shaft torque load; sgn(v) represents the sign of a relativespeed v between the control shaft and the input shaft; and f(T_(cam))represent the magnitude of the frictional torque T_(rq) _(—)_(function).
 8. The camshaft phase shifting device of claim 7 whereinSR₀ is calculated according to:${SR}_{0} = {\frac{N_{S\; 1}}{N_{S\; 2}} \cdot \frac{N_{P\; 2}}{N_{P\; 1}}}$where N denotes the number of gear teeth with its subscripts_(S1, S2, P1,) and _(P2) representing a first sun gear coupled to theinput shaft, a second sun gear coupled to the output shaft, a firstplanet gear engaged with the first sun gear, and a second planet gearengaged with the second sun gear, respectively; and wherein said firstand second planet gears are integral with a common planet carriercoupled to said control shaft.
 9. The camshaft phase shifting device ofclaim 1 wherein said frictional self-locking mechanism is configured fortransmitting torque from said input shaft to said output shaft; andwherein an application of torque to said control shaft controls saidfrictional self-locking mechanism to selectively unlock the phase angleof said input shaft relative to said output shaft.
 10. A method foraltering a camshaft phase angle for a camshaft driven though a camshaftphase shifting device including coaxially aligned input, output andcontrol shafts, wherein the input shaft and the output shaft arefrictionally phase-locked by said control shaft, comprising: regulatinga torque applied to said control shaft, wherein an application of torqueto said control shaft releases said frictional self-locking of saidinput shaft and said output shaft to unlock said input shaft phase fromphase-lock with said output shaft phase.
 11. The method of claim 10 foraltering a camshaft phase angle wherein said step of regulating saidtorque applied to said control shaft is responsive to at least one inputsignal selected from a set of input signals including, but not limitedto, a cam shaft phase angle error signal, a torque load signal, anangular position signal of the cam shaft, and relative speed signalbetween the input and output shafts.
 12. The method of claim 10 foraltering a camshaft phase angle wherein said step of regulating saidtorque applied to said control shaft includes controlling an electricmachine configured to exert an electro-magnetic torque on said controlshaft.